Molecular Mechanisms of Stem Cells Pluripotency and Cell Fate Specification

International audienc

Theory of spin-Hall magnetoresistance in the AC (terahertz) regime

In bilayers consisting of a normal metal (N) with spin-orbit coupling and a ferromagnet (F), the combination of the spin-Hall effect, the spin-transfer torque, and the inverse spin-Hall effect gives a small correction to the in-plane conductivity of N, which is referred to as spin-Hall magnetoresistance (SMR). We here present a theory of the SMR and the associated off-diagonal conductivity corrections for frequencies up to the terahertz regime. We show that the SMR signal has pronounced singularities at the spin-wave frequencies of F, which identifies it as a potential tool for all-electric spectroscopy of magnon modes. A systematic change of the magnitude of the SMR at lower frequencies is associated with the onset of a longitudinal magnonic contribution to spin transport across the F-N interface.Comment: 21 pages, 9 figure

Berlin's medical students' smoking habits, knowledge about smoking and attitudes toward smoking cessation counseling

Background: Diseases associated with smoking are a foremost cause of premature death in the world, both in developed and developing countries. Eliminating smoking can do more to improve health and prolong life than any other measure in the field of preventive medicine. Today's medical students will play a prominent role in future efforts to prevent and control tobacco use. Methods: A cross-sectional, self-administered, anonymous survey of fifth-year medical students in Berlin, Germany was conducted in November 2007. The study explored the prevalence of smoking among medical students. We assessed their current knowledge regarding tobacco dependence and the effectiveness of smoking cessation methods. Students' perceived competence to counsel smokers and promote smoking cessation treatments was also explored. Analyses were based on responses from 258 students (86.6% response rate). Results: One quarter of the medical students surveyed were current smokers. The smoking rate was 22.1% among women, 32.4% among men. Students underestimated smoking-related mortality and the negative effect of smoking on longevity. A considerable number of subjects erroneously assumed that nicotine causes coronary artery disease. Students' overall knowledge of the effectiveness of smoking cessation methods was inadequate. Only one third of the students indicated that they felt qualified to counsel patients about tobacco dependence. Conclusions: This study reveals serious deficiencies in knowledge and counseling skills among medical students in our sample. The curriculum of every medical school should include a tobacco module. Thus, by providing comprehensive training in nicotine dependence interventions to medical students, smokers will have access to the professional expertise they need to quit smoking

Strange matter prospects within the string-flip model

In this contribution we extend the recently developed two-flavor quark-matter string-flip model by including strange quarks. We discuss implications for compact stars.Comment: 4 pages, 4 figures, proceedings to SQM201

Stage-specific histone modification profiles reveal global transitions in the Xenopus embryonic epigenome.

Vertebrate embryos are derived from a transitory pool of pluripotent cells. By the process of embryonic induction, these precursor cells are assigned to specific fates and differentiation programs. Histone post-translational modifications are thought to play a key role in the establishment and maintenance of stable gene expression patterns underlying these processes. While on gene level histone modifications are known to change during differentiation, very little is known about the quantitative fluctuations in bulk histone modifications during development. To investigate this issue we analysed histones isolated from four different developmental stages of Xenopus laevis by mass spectrometry. In toto, we quantified 59 modification states on core histones H3 and H4 from blastula to tadpole stages. During this developmental period, we observed in general an increase in the unmodified states, and a shift from histone modifications associated with transcriptional activity to transcriptionally repressive histone marks. We also compared these naturally occurring patterns with the histone modifications of murine ES cells, detecting large differences in the methylation patterns of histone H3 lysines 27 and 36 between pluripotent ES cells and pluripotent cells from Xenopus blastulae. By combining all detected modification transitions we could cluster their patterns according to their embryonic origin, defining specific histone modification profiles (HMPs) for each developmental stage. To our knowledge, this data set represents the first compendium of covalent histone modifications and their quantitative flux during normogenesis in a vertebrate model organism. The HMPs indicate a stepwise maturation of the embryonic epigenome, which may be causal to the progressing restriction of cellular potency during development

Causal learning from interventions and dynamics in continuous time

Event timing and interventions are important and intertwinedcues to causal structure, yet they have typically been studiedseparately. We bring them together for the first time in an ex-periment where participants learn causal structure by perform-ing interventions in continuous time. We contrast learning inacyclic and cyclic devices, with reliable and unreliable cause–effect delays. We show that successful learners use interven-tions to structure and simplify their interactions with the de-vices and that we can capture judgment patterns with heuristicsbased on online construction and testing of a single structura

Ab initio Computation of the Static Exchange--Correlation Kernel of Real Materials: From Ambient Conditions to Warm Dense Matter

The electronic exchange-correlation (XC) kernel constitutes a fundamental input for the estimation of a gamut of material properties such as the dielectric characteristics, the thermal and electrical conductivity, the construction of effective potentials, or the response to an external perturbation. In practice, no reliable method has been known that allows to compute the kernel of real materials. In this work, we overcome this long-standing limitation by introducing a new, formally exact methodology for the computation of the static XC kernel of arbitrary materials exclusively within the framework of density functional theory (DFT) -- no external input apart from the usual XC-functional is required. As a first practical demonstration of the utility and flexibility of our methodology, we compare our new results with exact quantum Monte Carlo (QMC) data for the archetypical uniform electron gas model at both ambient and warm dense matter conditions. This gives us unprecedented insights into the performance of different XC-functionals, and has important implications for the development of new functionals that are designed for the application at extreme temperatures. In addition, we obtain new DFT results for the XC kernel of warm dense hydrogen as it occurs in fusion applications and astrophysical objects such as planetary interiors. The observed excellent agreement to the recent QMC results by B\"ohme \emph{et al.}~[Phys.~Rev.~Lett.~\textbf{129}, 066402 (2022)] clearly demonstrates that our framework is capable to even capture nontrivial effects such as XC-induced isotropy breaking in the density response of hydrogen at large wave numbers. Our method can easily be applied using standard DFT codes and will open up new avenues for the computation of the properties of real materials